1. Field of the Invention
The present invention relates generally to an ink pump control apparatus for printing presses, and more particularly to an ink pump control apparatus for controlling the revolution of an ink pump drive unit to control the feed rate of ink on the basis of printing speed and printing-image ratio (the ratio of printing-image area to the sum of printing-image area and non-image area).
2. Description of the Related Art
An ink pump control apparatus for controlling the revolution of an ink pump drive unit on the basis of printing speed and printing-image ratio to control the feed rate of ink has been disclosed in Japanese Patent Publication Nos. 2622072 and 2644181, for example.
The ink pump control apparatuses disclosed in these patent journals are designed to control the feed rate of ink by controlling the revolution of the ink pump drive unit in such a manner as to be proportional to printing speed in accordance with a predetermined coefficient for each printing-image ratio.
In ink feeding using an ink pump controlled in the aforementioned manner, printed materials of inappropriate printing densities tend to be produced due to differences in the degree of ink color development caused by changing the ink being in the accelerating stage at the start of printing and in the decelerating stage at the end of printing.
In ink feeding using an ink pump, ink is usually fed to the printing plate surface of the printing cylinder via an ink path comprising a plurality of rotating bodies such as an ink rail, an ink cylinder, an ink ductor, an ink form roller, etc.
In the accelerating stage at the start of printing, relatively long time is required until a sufficient amount of ink to print on a printing material with an appropriate printing density reaches the printing plate surface. As a result, printed materials of low printing densities tend to be produced.
In the decelerating stage at the end of printing, on the other hand, neither too much nor too little ink for printing at that point of time is retained on the surfaces of rollers and ink cylinders constituting the ink path. Nevertheless, as the printing press is decelerated to a halt, the number of printing materials to be printed in a unit of time is decreased rapidly. This results in an excessive amount of ink retained on the roller and cylinder surfaces, and the amount of ink supplied to the printing plate surface becomes more than the correct level, leading to generation of printed material of high printing densities.
The printing density of printing materials may vary because the degree of color development is apt to change with a change in ink color, or with a change in color pigment or solvent (that is, with a change in ink types) even when the ink is of the same color. As a result, even if the same amount of ink is fed, that is, even if the revolution of the ink pump drive unit is controlled in such a manner as to become proportional to printing speed in accordance with a predetermined coefficient, as described earlier, printing materials of inappropriate printing densities are often produced.
To cope with these inappropriate conditions, the operator can correct such improper printing densities by temporarily controlling the ink pump manually. Manual control, however, is not effective in reducing printed matter having improper printing densities because it involves extremely difficult operation requiring a lot of skill. Furthermore, it is a time-consuming operation because the state of printing has to be carefully observed during operation.
It is one object of the present invention to reduce running cost incurred due to production of a large amount of printed materials having improper printing densities by minimizing such printed materials having improper printing densities by automatically adjusting the feed rate of ink so that the printing density can be maintained at a proper level in the accelerating stage at the start of printing and in the decelerating stage at the end of printing, as described above.
It is another object of the present invention to reduce running cost incurred due to production of a large amount of printed materials having improper printing densities by minimizing such printed materials having improper printing densities by automatically adjusting the feed rate of ink in accordance with the degree of color development of the ink so that printing density can be maintained at a proper level even when the color of ink used varies, or even when ink used is of the same color but contains a different color pigment or solvent, that is, even when a different brand of ink is used.
The present invention provides an ink pump control apparatus used in a printing press where the feed rate of ink is caused to change by ink pumps based on printing image ratio and printing speed. The ink pump control apparatus comprises an image ratio input section to input data corresponding to the printing image ratio of an area to which ink is to be fed, a printing speed detecting section to detect the printing speed of the printing press and outputting a printing speed signal corresponding to the detected printing speed, a speed judgement section to judge a change in printing speed based on the printing speed signal output by the printing speed detecting section, a memory section to store first correction coefficients determined for different printing image ratios and third correction coefficients determined for the acceleration and deceleration of printing speed, and a processing section to fetch the first and third correction coefficients from the memory section based on the data corresponding to the printing image ratio and the judgement results of speed changes output by the speed judgement section, obtaining an ink feed correction coefficient from these coefficients and the printing speed, and outputting a signal for operating the ink pump so as to feed the amount of ink corrected by the ink feed correction coefficient; so that the operation of the ink pump is controlled based on the data corresponding to the printing image ratio and the judgement results of speed changes and the printing speed.
With the aforementioned construction, the printing image ratio of an area to which ink is fed by the ink pump is input into the processing section via the image ratio input section. Where ink type designation is needed, the designation of the type of ink to be used is input to the processing section by an ink designation section.
Upon receipt of a printing image ratio, the processing section fetches a first correction coefficient corresponding to the printing image ratio from among the first correction coefficients in the memory section. Where the type of ink used is designated, a second correction coefficient corresponding to the designated ink is fetched from among the second correction coefficients in the memory section.
In this state, the printing press is started. Then, printing press operating speed, that is, a signal corresponding to a printing speed is generated and input into the printing speed detecting section. The printing speed detecting section detects the printing speed of the printing press from the signal corresponding to the input printing press operating speed at predetermined time intervals, for example, and outputs a printing speed signal corresponding to the detected printing speed. The printing speed signal output by the printing speed detecting section is input into the speed judgement section and the processing section.
Upon receipt of the printing speed signal, the speed judgement section compares the currently input printing speed signal with a previously input printing speed signal to judge whether the printing speed is accelerated or decelerated, or remains unchanged, and outputs the judgement result in the form of a signal. The signal output by the speed judgement section is input into the processing section.
The processing section, to which the printing speed signal and the signal of the printing speed judgement result are input following the start of the printing press, fetches a third correction coefficient corresponding to the input printing speed judgement result from among the third correction coefficients in the memory section, and decides the first, second and third correction coefficients based on the printing speed signal. Furthermore, the processing section calculates an ink feed correction coefficient based on the determined first, second and third correction coefficients, and outputs a signal for operating the ink pump to feed the amount of ink corrected with the obtained ink feed correction coefficient.